The long-range goal of this project is to delineate the mechanisms involved in the regulation of the synthesis and metabolism of cyclic nucleotides in E. coli. Our recent findings showed that the system for sugar transport referred to as the phosphoenolpyruvate:sugar phosphotransferase system (PTS) plays a role in the regulation of adenylate cyclase. We proposed that Enzyme I of the PTS serves as a regulator of adenylate cyclase. Support for the model that the phosphorylated state of Enzyme I is associated with a condition of stimulation of adenylate cyclase activity comes from studies showing that glucose or pyruvate inhibit adenylate cyclase activity, while phosphoenolpyruvate stimulates the activity. We have also begun to explore the mechanism by which sugars transported by a mechanism involving protonmotive force inhibit adenylate cyclase. Lactose transport is coupled to the inhibition of adenylate cyclase activity only if the proton symport mechanism is also active. Our current hypothesis is that adenylate cyclase can be inhibited by two mechanisms. Transport of of PTS sugars decreases the steady-state level of the phospho-form of the PTS protein Enzyme I; transport of sugars linked to a proton symport mechanism decreases the proton gradient. Either of these effects produces inhibition of adenylate cyclase activity.